What is an automated underwriting system?
An automated underwriting system evaluates a loan file against guidelines and returns a decision automatically. It says approve, review, or rejected, and it attaches findings and conditions. Agency underwriting does this for agency loans. A non-agency AUS does it for everything outside that box, against the lender’s own rules.
How an AUS turns a loan file into a decision
An AUS is a rules engine pointed at a loan file. It works in four steps, and only the last one involves a person.
Data in. Credit, income, assets, property, and the product the borrower applied for.
Rules run. The engine compares that data to the guideline set that applies.
Findings out. Approve, review, or rejected, plus the conditions that still have to clear.
A person clears what the rules cannot. Exceptions, missing docs, and judgment stay human.
Same file, same rules, same answer. That is the point of an AUS: two underwriters can read one file two ways. A rule set cannot.
Agency underwriting and non-agency AUS: the difference is who writes the rules
Agency underwriting runs agency guidelines. A non-agency AUS runs yours. That one difference decides which loans each system can underwrite.
Agency underwriting covers agency-eligible conventional files. It cannot run your overlays, Non-QM, or business purpose. A non-agency AUS covers any program you can write as a rule. Nothing the guideline can express is out of reach.
Agency AUSs are excellent at the job they were built for. They are not broken. They were never meant to underwrite a bank-statement file or a DSCR rental.
The loans that have no AUS
Agency underwriting only accepts loans that fit agency eligibility. Every loan type below falls outside it, so the guideline lives in a PDF and an underwriter applies it by hand.
Non-QM overlays. Bank statement, asset depletion, 1099, P&L. Each investor writes a different credit box.
Business purpose. DSCR, fix and flip, bridge, construction. Underwritten on property cash flow, rehab, or exit, not agency income.
Portfolio and specialty. Manufactured housing, member programs, held-for-investment books your core system never learned.
Outside the agency box, the “AUS” has been a person with a PDF.
What AUS does with that gap
AUS is a non-agency automated underwriting system. You write the credit policy as rules. The engine returns a decision with findings and conditions in real time. PricingEngine can run on those rules. PMIPricer quotes MI from the same file, no re-keying. Read more on types of automated underwriting systems, agency vs non-agency AUS, and manual underwriting.